scale

In chemistry, calcium carbonate precipitates that form on the inside of a kettle or boiler as a result of boiling hard water (water containing concentrations of soluble calcium and magnesium salts). The salts present in hard water also precipitate out by reacting with soap molecules.

Scale may cause damage to water pipes and appliances such as washing machines and water boilers. The build-up of scale causes blockage of pipes, and electrical appliances have to use more electrical energy to operate efficiently.